Conventional Selective Catalytic Reduction (SCR) of NOx involves injection of a typically aqueous urea solution into the exhaust system ahead of the SCR catalyst. Although this technology allows a steady state NOx conversion efficiency of  greater than 90%, transient test cycle NOx conversion efficiencies of only about 80% conversion efficiencies have been achieved. However, this is insufficient given that emission standards for 2007 and beyond will require transient test cycle NOx conversion efficiencies of better than 95%.
Moreover, there are several shortcomings with the current SCR technology. First, current SCR systems only work effectively over an exhaust temperature range of about 275xc2x0 C. to about 450xc2x0 C. This means that it cannot be utilized under light load conditions or under high load conditions. Second, it is difficult to match the transient response of the catalyst system to that of the engine over the transient test cycle, resulting in a loss of conversion efficiency or ammonia slip. Third, effectively mixing the urea solution with the exhaust gases may be problematic. Fourth, the precious metal loading of the catalyst makes the catalyst system very expensive.
Although the reduction of NOx through the injection of urea or ammonia compounds directly into the combustion chamber of an engine has been accomplished without a catalyst using a method called Selective Non-Catalytic Reduction (SNCR) and is available at all speeds and for all types of loads, only a 20% to 50% NOx conversion efficiency has been acheived. Unfortunately, this too is insufficient and does not satisfy the future transient test cycle NOx conversion efficiency requirement of circa 95%.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a reductant injection system for an internal combustion engine comprising: a selective reduction system communicated with the internal combustion engine; a vehicle sensor communicated with the internal combustion engine; a controller, wherein the controller is communicated with the selective reduction system and the vehicle sensor and a reductant storage device communicated with the selective reduction system.
A method for increasing NOx conversion efficiency in an internal combustion engine having a reductant injection system, comprising: obtaining a vehicle data signal responsive to the engine performance of the internal combustion engine; processing the vehicle data signal so as to determine a combustion characteristic of a combustion cylinder; determining an optimum reductant injection timing and introducing a predetermined amount of reductant into the combustion cylinder responsive to the optimum reductant injection timing.
A medium encoded with a machine-readable computer program code for increasing NOx conversion efficiency in an internal combustion engine having a reductant injection system, the medium including instructions for causing controller to implement the aforementioned method.